The present invention relates to a digital pipelined heterodyne circuit for heterodyning a data input signal by a signal of a predetermined frequency.
Heterodyning is a technique that has application in many areas of communiations and signal processing. For example, in spectrum analysis, it is often necessary to shift the center frequency of a broad-band signal into a region where a narrow-band filter may be located which is used to sample input data. In order to accomplish this function, digital heterodyne circuits are available which digitize a data input signal and multiply that signal by the sine and cosine components of a user-chosen reference signal having a predetermined frequency. The problem with such circuits is that each data byte must be digitally multiplied by digital sine and cosine coefficients one at a time. Digital multiplication is a two-step process involving the combining of one bit of the sine and cosine coefficient with the data byte in an AND-gate array and then adding the product to the previous product formed by the previous gate array. It will take as many steps to completely multiply the data byte as there are bits in the sine and cosine coefficients. For example, if there are m significant bits, each data input byte must be processed, one bit at a time, m times, before the next byte can be processed. This leads to unacceptably slow processing time, especially if high resolution is required.